1. Field of the Invention
The present invention is related to a double head supporting mechanism for a magnetic disk drive, and particularly to a double head supporting mechanism for a magnetic disk drive with improved in performance to follow or track the upward and downward swell bias (deviation due to swaying in the vertical directions) caused during the rotation of magnetic disk drive, as well as in read/write quality.
2. Description of the Prior Art
As an external memory element of a computer, various types of magnetic disks are used, and they are in practical use in the form of a hard disk or a floppy disk.
In such disks, the necessary information is magnetically recorded on concentric circles along the surface of the magnetic disk. Also, random readout can be made freely from the magnetic disk. In order to enable such read/write performance, a magnetic disk drive is provided with a head supporting and feeding mechanism that serves to move and position the read/write head to and at the specified track along the rotating magnetic disk.
Usually, the above described hard disk is fixed in the body of the disk drive, in a sealed state and in a rotatable manner. On the other hand, the floppy disk is itself able to be inserted in and removed from the disk drive. However, for both cases, the read/write head must be supported on the disk surface securely, with a specified micro gap maintained in between or in a closely contacted manner. Accordingly, the head supporting mechanism as described above exerts a significant effect on the read/write characteristics.
Recently, the floppy disks in use have been reduced in size at a quick pace, from the conventional 8 inch type to the 5.25 inch or 3.5 inch type. As a result, their information recording density has increased markedly. Therefore, the proper positioning of the head when the foregoing disk surface and the head are in contact with each other is of vital importance.
Furthermore, the magnetic disk drive used presently is itself required to be small in size, and for a portable or transportable magnetic disk drive that is small in size and high in density, the role played by the head supporting mechanism has vital significance in maintaining constantly stable read/write characteristics.
Specifically, there has been the problem that, when a so called off-track in which the read/write head becomes positionally deviated in the direction of the magnetic disk diameter from the specified track is caused, sufficient reading output cannot be obtained thereby causing a read and write failure. The occurrence of such offtrack positioning not only depends on the bias caused during the assembly of the read/write head, but it also depends largely upon the pitch with which the head follows the swell bias (swaying deviation) in the upward and downward directions when it occurs during the rotation of the magnetic disk. Consequently, various types of head supporting mechanisms with a design to restrain the aforedescribed offtrack positioning incorporated in them have been provided.
The first of such systems offered conventionally is shown in U.S. Pat. No. 4,151,573 (Japanese patent Gazette No. 58-15866). The structure in this system is as follows. In order to hold the heads in close contact with both surfaces of the floppy disk, the lower head is unmovably fixed to the carriage, while the upper head is held against the arm by a gimbal support.
In this first conventional system, since the lower head is itself fixed to the carriage, its read/write surface provides the reference plane for reading from the floppy disk. Thus, the flexible floppy disk is forcibly caused to follow the lower head surface by the loading pressure given by the upper head, and in this manner, the swelling (waving) of the floppy disk is eliminated.
The second system proposed conventionally is to make the double-sided heads follow up and down the magnetic disk surfaces, respectively. For example, as proposed in the U.S. Pat. No. 4,355,339 (Japanese patent Gazette No. 56-98746), both heads are respectively held rotatably against the carriage, and in this way, each of the heads follows separately the vertical swelling of the magnetic disk.
The foregoing conventional systems, however, have been troubled with the problems described below. In the first system described above, because the lower head provides the fixed reference plane, the floppy disk is always forced to deform in order to follow the reference plane, with the specific drawback of a high degree of abrasion caused between the lower head and the disk surface. In addition, due to errors in manufacturing or assembly, the floppy disk carries with it a variance in height that is not negligible, when it is inserted into the drive. In the first system provided conventionally, the floppy disk having such vertical variance is made to follow the common, single reference plane. As a result, the extent of biting of the lower head into the disk face, that is usually known as penetration, differs for each floppy disk. Such forcible deformation caused to the disk not only invites the afore described abrasion, but also seriously and adversely affects the reading quality, and relatively extensive offtrack positioning is caused to each magnetic disk.
In the second system provided in the past, while the following or tracking performance of the magnetic disk is improved, because the rocking arms for fixing the respective heads are supported by the carriage separately to each other, the movements of the upper and lower arms when they follow the upward and downward swaying deviation of the magnetic disk are not uniform. As a result, variance is caused between the upper and lower heads in their offtrack positioning. Thus, it is difficult in practice to restrict the extent of the offtrack positioning of both of the heads within a preferred range.